Abstract
The LLC (inductor-inductor-capacitor) converter is the widely used soft-switching resonant DC-DC converter. As a multi-resonant, variable-frequency converter, the LLC converter modeling is complex. Several methods have been proposed for modeling and controlling the LLC converter in literature. In this paper, the Synchronous Reference Frame (SRF) based modeling approach is proposed which helps to derive a simplified model for switching frequency to output voltage transfer function in the case of LLC converter. The dominant circuit parasitic elements such as secondary side semiconductor switch drop, dc resistance (DCR) of resonant inductor and transformer, and equivalent series resistance (ESR) of output capacitor are incorporated into the SRF model. Inclusion of these parasitics results in an accurate LLC converter model. The derived model is used to design controller for Voltage Mode Control (VMC) of LLC converter. This controller is implemented using 16-bit Digital Signal Controller (DSC). The proposed model and digital controller are verified through experiments. The model prediction and experimental frequency response plots are found to be in good agreement.
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